共查询到19条相似文献，搜索用时 187 毫秒
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卫民 《沉积与特提斯地质》1997,17(6):55-61
实验室实验说明，某些介形虫是肉食的，它们是血吸虫病媒体钉螺的有效杀灭者。介形虫的繁殖是十分快的，在自然界可以迅速增加数量，达到足够的密度。由此推测，介形虫可以应用于血吸虫病的生物防治。这不仅在科学研究上具有重大理论意义，而且在卫生防疫上具有重要实用价值。 相似文献
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取水枢纽是供水工程最重要的组成部分,形式多样。研究陇县供水工程段家峡水库取水枢纽的取水方式及选取问题,通过对总干渠取水、放水洞取水、泵站取水等方案进行分析论证,确定合理的取水方案,认为由坝后灌溉总干渠取水方案最合理。为其它由水库供水的类似工程设计和建设提供参考。 相似文献
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玛河位于新疆天山地带,属于核心区域,在水资源项目开发建设的过程中存在问题。本文通过对流域地下水资源开发利用现状、取水中存在问题进行分析,提出应加强取水过程中控制措施,通过建立专门的取水管理机构、依据取水原则全面控制取水量、建立先进水源地管理建设方案、对供水价格进行控制、实施合理先进的取水量计量方式以及建设完善的取水保障制度等措施,在增强取水管理力度的基础上,加大水源地的建设力度,对水资源进行合理的利用与配置,保证水资源开发的科学性与合理性,提高工作水平,达到预期工程开发建设目的。 相似文献
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按照水利部县级总体实施方案水资源论证要求,取水水源论证主要内容包括取水方案合理性分析和取水可靠性分析。文章以辽中县“节水增粮行动”取水方案为研究对象,分析论证了其合理性。辽中县地处辽河中下游平原区,“节水增粮行动”项目片区分布全县8个乡镇,项目片区面积2 766 hm2,取水方案为就地取用地下水。在已有水文地质资料的基础上,结合抽水试验数据,分析得出了论证区单井涌水量、影响半径等水文地质参数,通过确定每个区域的单井涌水量,对方案中单井的控制面积和井数进行了复核,分析认为方案合理可行。 相似文献
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在分析区域水文地质条件及水资源开发利用状况的基础上,对青海省西南部某金矿建设项目确定水资源论证等级及论证范围,并进行取用水合理性分析,论证取水水源的可靠性与可行性,分析取水和退水的影响。结果表明:该金矿建设项目取用水合理,取水水源可靠可行,建设项目取退水对区域水资源和其他用户基本无影响。为取水许可的科学审批提供技术依据。 相似文献
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Summary This paper deals with the effects of air leakage from intake to return airways through a series of stoppings on the analysis of coal mine ventilation. The mathematical model which assumes continuous leakage along adjoining intake and return airways is reviewed, and a new mathematical approach is presented based upon the concentrated leakage through individual stoppings. The procedure incorporating the new method in the analysis of coal mine ventilation networks is also discussed. 相似文献
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Drinking water-type fluorosis is the most harmful endemic disease in China with the largest number of sufferers. Although the implementation of the policy to alter water sources to lower fluoride level has effectively controlled the spread of this kind of endemic disease, its prevalence could not thoroughly be stopped because the high-fluoride environmental background in these endemically diseased areas could still do harm to human health through food chain. Therefore, it is necessary to conduct a more deep-going study on the drinking water-type fluorosis. To investigate the effect of high fluorine environmental background on crops and human health in the hot spring-type fluorosis-diseased areas, local water, paddy soil, rice, whole vegetables and soils around their roots were sampled for analysis. The results were compared with those of the control groups in fluorosis-free areas which are similar to the fluorosis-diseased areas both in natural background and in social background. It is indicated that rice and vegetables can accumulate water-soluble fluorine either in soils or in irrigating water, and different crops have different abilities of fixing fluorine. The contents of fluorine in different parts of vegetables in the fluorosis-diseased and fluorosis-free areas were statistically categorized. The results showed that the fluorine contents of roots, tubers, leaves and flowers of vegetables in the fluorosis-diseased areas are 3.56, 1.17, 3.07 and 3.23 mg/kg, respectively. However, comparisons showed that in the fluorosis-free areas, the fluorine contents are 2.17, 0.70, 1.91 and 2.52 mg/kg, respectively. Moreover, different parts of a crop also show significantly different fluorine fixation abilities. It is demonstrated that the fluorine contents of the strongly metabolic parts are relatively high. For example, the fluofine contents of roots, leaves and flowers of vegetables are much higher than those of stems. The fluorine fixation ability of seeds is very weak. In order to reduce the risk of human body＇s 相似文献
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The introduction and spread of smooth cordgrass (Spartina alterniflora) in South San Francisco Bay 总被引：1，自引：0，他引：1
Spartina alterniflora was first introduced into south San Francisco Bay in the 1970’s. Since that time it has spread to new areas within the south bay and is especially well established at four sites. The spread of this introduced species was evaluated by comparing its vegetative and reproductive characteristics to the native cordgrass, Spartina foliosa. The characters studied were intertidal distribution, phenology, aboveground and belowground biomass, growth rates, seed production, and germination rates. Spartina alterniflora has a wider intertidal distribution than S. foliosa and outproduced the native cordgrass in all aspects that were studied. These results indicate that the introduced species has a much better chance of becoming established in new areas than the native species, and once established, it spreads more rapidly vegetatively than the native species. Spartina alterniflora is likely to continue to spread to new areas in the bay and displace the native plant. In addition, this introduced species may effect sedimentation dynamics, available detritus, benthic algal production, wrack deposition and disturbance, habitat structure for native wetland animals, benthic invertebrate populations, and shorebird and wading bird foraging areas. *** DIRECT SUPPORT *** A01BY058 00013 相似文献
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This paper presents a new geotechnical design concept, called robust geotechnical design (RGD). The new design methodology seeks to achieve a certain level of design robustness, in addition to meeting safety and cost requirements. Here, a design is considered robust if the variation in the system response is insensitive to the variation of noise factors such as uncertain soil parameters and construction quality. When multiple objectives are considered, a single best design may not exist, and a trade-off may be necessary. In such a case, a genetic algorithm is adopted for multi-objective optimization and a Pareto Front, which describes a trade-off relationship between cost and robustness at a given safety level, is established. The new design methodology is illustrated with an example of spread foundation design. The significance of the RGD methodology is demonstrated. 相似文献
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中国北方东部沙质荒漠化的地学观 总被引：8，自引：2，他引：8
中国北方东部的土地荒漠化主要受新构造运动以来的权造－沉积特征、青藏高原隆升所引起的全球气候变化、尤其是亚洲季风等地质背景控制。北方东部沙质荒漠化区域地质分类，按其成因可分为就地起沙型、风沙型和土地粗粒化型等3种类型。其中，就地起沙型沙质荒漠化主要分布在东部毛乌素、科尔沁、浑善达克、呼伦贝尔等沙地内，流经这些沙地的古河道，广泛发育河湖相砂质沉积物以及以砂质沉积物为母质的土壤分布区。风沙型沙质荒漠化主要分布在上述沙地的边缘地带，如毛乌素沙地以南的覆沙黄土区等。土地粗化主要分布在内蒙古锡林郭勒草原－河北坝上草原－河北坝上草原，其土壤类型多为含砾沙土，其土壤母质为基岩风化壳、残坡积或冲洪积物。荒漠化发展趋势上，尽管就地起沙型沙质荒漠化在毛乌素、科尔沁和浑善达达沙地的局部地区均有所逆转，但总体上，在北方广大地区，主要以地表土壤粗化为主的荒漠化和风沙型荒漠化等均有不同程度的扩大。上述不同类型的沙质荒漠化，总体上受地背景控制。其中，第四纪以来的构造－沉积特征控制着不同类型荒漠化的区域分布，气候变化控制着荒漠化的进程，人类活动则是在上述背景的基础上进行。 相似文献
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Nano Ruzin 《GeoJournal》2000,52(2):353-357
The authority of Marshall Tito and his newly crafted iconography of `brotherhood and unity' temporarily marginalized the ethnic deographies of the peoples in the Yugoslav Federation. In the 1990s this Yugoslavia was run over by time. The Republic of Macedonia was among the newly emerging states. In Macedonia the multi-ethnic mosaic was complicated by the confusion of old and new iconographic impulses. In 2001 the Macedonian crisis developed as a result of the spread of the new regional Albanian identity spread by the domino effect to the areas with mixed population in the Balkans after the events in Kosovo. Differences between Macedonians and Albanians are analyzed in terms of family structure, religion and ethnic and national affiliation. The politics based on these cleavages and their ensuing, contested iconographies are set out. 相似文献
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High precision design wave height is required in extreme marine environments in typhoon-affected sea areas. A new model is built under typhoon effect to calculate the design wave heights. The new model has multiple undetermined parameters, and it is able to fit observed data more flexibly and accurately. In addition, the distribution functions of this new model are based on the maximum entropy principle. Therefore, they can avoid the apriority, which means arbitrarily assigning Poisson distribution to describe the distribution of typhoon occurrence frequency and assigning Gumbel distribution or Pearson-III distribution to describe the distribution of extreme events in the process of applying the compound distribution to deduce the design elevations. The observed data of 18-year (1984–2001) extreme wave heights and the corresponding typhoon events in Maidao are used to test the model. Test results show that the new model is theoretically more stable and more precise when predicting the design wave heights under the typhoon-affected sea areas. 相似文献
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四川德阳地区农田生态系统重金属健康风险评价 总被引：4，自引：1，他引：3
环境健康风险评价是定量描述环境中污染物对人体产生健康危害的风险的重要方法。文中结合国内外健康风险评价理论,利用美国环保总署健康风险评价模型,计算了四川德阳地区居民经呼吸(大气颗粒物)、食入(粮食)、饮用(饮用水)和皮肤接触途径摄入重金属而引起的健康风险。研究结果显示:德阳地区所有市县的非致癌风险指数都大于1,表明存在一定的风险。绵竹和旌阳区的风险最高,二者的非致癌风险指数分别达到7.76和4.36。从不同暴露途径的贡献来看,主要是经食物暴露的贡献,各市县都达到了90%以上。虽然计算结果存在一定的不确定性,但对研究区进行风险管理具有重要的参考价值。 相似文献